/*
 * UniformDistribution.java
 *
 * Copyright (C) 2002-2006 Alexei Drummond and Andrew Rambaut
 *
 * This file is part of BEAST.
 * See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership and licensing.
 *
 * BEAST is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 *  BEAST is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with BEAST; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA  02110-1301  USA
 */

package dr.math;

/**
 * uniform distribution.
 *
 * @version $Id: UniformDistribution.java,v 1.3 2005/07/11 14:06:25 rambaut Exp $
 *
 * @author Andrew Rambaut
 * @author Alexei Drummond
 */
public class UniformDistribution implements Distribution
{
	//
	// Public stuff
	//

	/**
	 * Constructor
	 */
	public UniformDistribution(double lower, double upper) {
		this.lower = lower;
		this.upper = upper;
	}

	public double pdf(double x) { return pdf(x, lower, upper); }
	public double logPdf(double x) { return logPdf(x, lower, upper); }
	public double cdf(double x) { return cdf(x, lower, upper); }
	public double quantile(double y) { return quantile(y, lower, upper); }
	public double mean() { return mean(lower, upper); }
	public double variance() { return variance(lower, upper); }

	public final UnivariateFunction getProbabilityDensityFunction() { return pdfFunction; }

	private UnivariateFunction pdfFunction = new UnivariateFunction() {
		public final double evaluate(double x) { return pdf(x); }
		public final double getLowerBound() { return lower; }
		public final double getUpperBound() { return upper; }
	};


	/**
	 * probability density function of the uniform distribution
	 *
	 * @param x argument
	 * @param lower the lower bound of the uniform distribution
	 * @param upper the upper bound of the uniform distribution
	 *
	 * @return pdf value
	 */
	public static double pdf(double x, double lower, double upper) {
		return (x > lower && x < upper ? 1.0 / (upper - lower) : 0.0);
	}

	/**
	 * the natural log of the probability density function of the uniform distribution
	 *
	 * @param x argument
	 * @param lower the lower bound of the uniform distribution
	 * @param upper the upper bound of the uniform distribution
	 *
	 * @return log pdf value
	 */
	public static double logPdf(double x, double lower, double upper) {
        return Math.log(pdf(x, lower, upper));
	}

	/**
	 * cumulative density function of the uniform distribution
	 *
	 * @param x argument
	 * @param lower the lower bound of the uniform distribution
	 * @param upper the upper bound of the uniform distribution
	 *
	 * @return cdf value
	 */
	public static double cdf(double x, double lower, double upper) {
        if (x < lower) return 0.0;
        if (x > upper) return 1.0;
        return 1.0 * ((x - lower) / (upper - lower));
	}


	/**
	 * quantile (inverse cumulative density function) of the uniform distribution
	 *
	 * @param y argument
	 * @param lower the lower bound of the uniform distribution
	 * @param upper the upper bound of the uniform distribution
	 *
	 * @return icdf value
	 */
	public static double quantile(double y, double lower, double upper) {
        if (y >= 0.0 && y <= 1.0) throw new IllegalArgumentException("y must in range [0,1]");
        return (y * (upper - lower)) + lower;
	}

	/**
	 * mean of the uniform distribution
	 *
	 * @param lower the lower bound of the uniform distribution
	 * @param upper the upper bound of the uniform distribution
	 *
	 * @return mean
	 */
	public static double mean(double lower, double upper)
	{
		return (upper + lower) / 2;
	}

	/**
	 * variance of the uniform distribution
	 *
	 * @param lower the lower bound of the uniform distribution
	 * @param upper the upper bound of the uniform distribution
	 *
	 * @return variance
	 */
	public static double variance(double lower, double upper)
	{
		return (upper - lower) * (upper - lower) / 12;
	}

	// Private

	private final double upper;
    private final double lower;

}
